Current and next-generation optical networks require ultrahigh transmission speeds and fast packet switching to support a growing need for multimedia applications. Advances in fiber-optic technology (e.g., erbium-doped fiber amplifiers (EDFAs), high-speed time multiplexing/demultiplexing, high density wavelength division multiplexing (WDM) devices, optical tunable filters, etc.) have led researchers to envision a future all-optical network that is capable of supporting multiple access and services at a very high bit rate.
In such all-optical multi-access networks, any node can use a designated time slot to send a packet to some other nodes. One significant difference between an all-optical multi-access network and a conventional point-to-point link is that the amplitude and phase of the received packets in an all-optical multi-access network may be quite different from packet to packet due to different fiber attenuation and the chromatic dispersion caused by the variation of the transmitters' wavelengths. For example, the amount of amplitude variation between two bursts of data packets can be as high as 10-20 dB.
Some related art receivers are not suitable for burst-mode operation because they cannot instantaneously handle the different arriving packets with large difference in optical power. It is therefore desirable to design receivers that can adapt to the variation in optical power on a packet-by-packet basis. These types of receivers are commonly referred to as burst-mode receivers, which are generally either of the feedback type or the feedforward type.
The feedback type receiver uses a differential transimpedance amplifier with a peak detection circuit to form a feedback loop. The peak detector circuit determines the instantaneous detection threshold for the incoming optical signal. The preamplifier extracts the signal's amplitude, and is DC-coupled at the output to a differential post-amplifier for further amplification. While a feedback loop enables the receiver to work more reliably and accurately, feedback loops increase the time required to settle to a final value. They also introduce additional circuitry which increases power dissipation.
In feedforward type receivers, the received optical signal is first amplified by a DC-coupled preamplifier and then output to a differential amplifier and fed forward into a peak detection circuitry to recover the amplitude of received packets. The peak detector determines a proper threshold level that may be set in front of the differential amplifier. At the output of the differential amplifier, the amplitude-recovered data packet is ready for further processing. As this scheme does not employ a feedback loop, the circuitry needs to be carefully designed to prevent oscillation in the receiver. This type of design introduces compromises: a fast settling system will, for example, introduce baseline wander that will degrade receiver sensitivity.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore this Background section may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.